The invention relates to a method of manufacturing the silica nanopowders with biocidal properties, especially for polymer composites.
The high requirements for materials used in such fields as medicine (equipment, room equipment, protective clothing, prostheses), textile and footwear industry, household goods, plastics, paints, lacquers, are the reason of the intensification of research on obtaining the high molecular mixtures having bactericidal and/or fungicidal properties.
From the scientific literature there is known the use of colloidal silver solutions as a biocide additive for different materials such as plastics, coated fabrics etc. It was found that biocidal properties of colloidal silver solutions occur already at the concentration of 1 ppm (Gaisford S., Blezer A. E., Bishop A. H., Walter M., Parsons D. International Journal of Pharmaceutics 2009, 366, 11-116). In several publication the authors stress that the problem occurring in the use of colloidal silver is the agglomeration of silver particles and their coagulation, hampering to a large extend obtaining the required biocidal activity (Halbig P., Gran H., Nickel U. Photochem. Photo-biol. 1994, 60 , 605; Schktcliff N., Nickel U., Schneider S., J. Colloid Interface Sci. 1999, 211, 122; Rivas I., Sanchez-Cortes S., Garcia-Ramos J. V., Morcillo G., Langmuir 2001, 17, 574; Nickel U., Castell A Z., Poppl K., Schneider S., Langmuir 2000, 16, 9087). Silver nanoparticles have significantly higher biocidal activity than silver microparticles. The achievement of biocidal activity in the case of silver microparticles requires the use of concentration 103 higher than in the case of the concentration of silver nanoparticles to obtain the acceptable biocidal activity (Damm C., Munstedt H., Rosch A., Materials Chemistry and Physics 2008, 108, 61-66).
Sharma V. K., Yngard R A., Lin Y., Advances in Colloidal and Interface Sci 2009, 145, 83, described the studies on the methods of the stabilization of colloidal silver particles with the use of protective colloids or by fixation in polymer particles. The use of such stabilized silver colloids is limited due to the unfavorable effect of stabilizers on the properties of obtained material.
From patent specifications U.S. Pat. No. 6,482,444, U.S. Pat. No. 6,495,257 and US 2006/0246149 there also known powders, comprising of particles, e.g. SiO2, comprising microparticles of metal compounds, i.a. zinc oxide, silver oxide. These powders characterize with higher grain sizes (than nanoparticles), and in that the microparticles of metal compounds are inside the particles.
There is known a process of manufacturing, by sol-gel method, of spherical SiO2 particles, containing inclusions nanometric silver particles, described and Polish Patent application P-360190. The sizes of silica powder grains is in the range of 200 to 800 nm. However it is not possible to obtain with that method the silica nanopowders of the sizes below 200 nm, containing nanoparticles of metallic silver. It is a significant limitation in their use as nanofillers of polymer composites.
The unique properties of polymeric nanocomposites are connected with small dimensions of nanofiller particles and they differ distinctly from the properties of composites obtained from particles above 200 nm. Nanocomposites obtained just from some percent contents of nanofillers (0.5-5%) show specifically preferred properties, i.a. improved barrier properties as well as much higher mechanical and optical properties, better thermal and chemical resistance, reduced flammability and smaller coefficient of linear expansion. To obtain the similar effect with the use of conventional fillers it is necessary to use them in significant amount (from 10 to several dozen percents).
From the patent specification PL 198 188 there is known a process of manufacturing, by sol-gel method, of silica nanopowders with small polydispersity of particle size, including functionalized ones. The size of silica nanopowder obtained with the described process depends on the amount of used catalyst and the composition of the reaction mixture. The polymeric nanocomposites obtained with the use of such nanopowder show very good physico-mechanical properties, especially with the use of functionalized nanopowder, durably embedded in the polymer matrix.